Apparatus for multiple grinding



Aug. 26, 1952 H. H. MORRIS APPARATUS vFOR MULTIPLE GRINDING Filed Dec. 22, 1950 9 Sheets-Sheet l NN@ @mx wmY E mm n@ www Aug. 26, 1952 H. H. MORRIS 2,608,033

APPARATUS FOR MULTIPLE GRINDING Filed Dec. 22, 195o 9 Sheets-sheet 2 Tag?.

ORNEYS Aug. 26, 1952 H. H. MoRRls 2,608,033

APPARATUS FOR MULTIPLE GRINDING Filed Dec. 22. 1950 9 Sheets-Sheet 3 "..e ai

j INVENTOR an@ ,5M/g

ATTORNEYS Aug. 26, 1952 v H. H. MORRIS 2,608,033

APPARATUS FOR MULTIPLE GRINDING I Filed Dec. 22. 1950 9 Sheets-Sheet 4 Ill/1 2 4 am 26 f6 292 g5 14p- 15 Z 254 5%WM/ K ATTORNEYS Aug. 26, 1952 H. H. MORRIS l 2,608,033

APPARATUS FOR MULTIPLE GRINDING Filed Dec. 22, 1950 9 Sheets-Sheet 5 T1 EIR..

INVENTOR ww ATTORNEYS Aug. 26, 1952 H. H. MoRRls APPARATUS FOR MuLTxPLE GRINDING 9 Sheets-Sheet 6 Filed Dec. 2.2. 1950 www mM N e TTORNEYS Aug- 26, 1952 H. H. MORRIS 2,608,033

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NVENTOR j/144e@ A( @ee/ BY W ATTORNEYS Aug. 26, 1952 H. H. MORRIS APPARATUS FOR MULTIPLE GRINDING 9 Sheets-Sheet 9 Filed Dec. 22, 1950 MYUL.

Patented Aug. 26, 1952 UNITED STATES PATENT OFFICE (Granted .under the act of March k3, 1883, as amended April 30, 1928;'1370 G. G. 75,7)

-22 Claims.

|This invention relates to a machine tool for grinding a number of work pieces simultaneously. It is applicable, for example, to grind the surfaces of air foils and blades, such for example as are used in jet engines for aircraft propulsion, gas turbines, and the like. It is especially well adapted to finish-grind simultaneously a plurality of blades that have been forged or cast and which must be nished to more precise contour.

Difficulty has been encountered in tlf-iis field due to the slowness of the finish-grind opera tion and its high cost.- When attempting to nnish-grinda plurality of blades simultaneously a major problem has been how to compensate for -the wear on the grinding surfaces which causes receding of the grinding surfaces from the work pieces respectively and a change in the radii of the grinding surfaces relative to the follower.

An object of the invention is to provide a 4inachine tool which is capable of simultaneously grinding a plurality of blades to close tolerances and at Vrelatively low unit cost.

Another object of the invention is to provide means in a multiple grinder for maintaining the grinding wheels true and accurate in regard to contour and position with respect to a follower wheel.

Another object of the invention is to provide a multiple grinder with means for vcompensating for grinding Wheel wear.

Other objects of the invention Will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, lcombinations of elements, arrangements'of parts, and in the several steps and relation. and order of each of said steps, to one or vmore of the others thereof, all as will be pointed out in the following description, and the scope of the application of which will 4be indicated in the following claims.

The invention will best be understood if the following description is read in connection with the drawings, in which,

vFigure 1 is a top plan view of the embodiment of the grinding machine in which the master template and the work pieces are lcompletely revolved;

Figure 2 is a fragmental plan view showing the cycle timing hook-up for controlling the means for dressing the grinding wheels;

Figure 3 is a fragmental side view of timing means for lengthening the connecting pantograph arms to retract the wheels from work 2 Y during the grinding wheel dressing operation;

Figure 4 is a vertical cross section taken 4on the line 4 4 of Figure 1;

Figure 5 isa detail view taken on the `line E-- of Figure 4;

Figure 6 is a vertical cross section taken on the line 6--6 of Figure 1; Y

Figure 7 is a top plan section taken on the line l-I of Figure 6;

Figure 8 is a horizontal section taken on the line 8--8 :of 'Figure 1;

Figure i9 is a fragmental diagrammatic view :of the air vcylinders and pistons for `maintaining the follower wheel in contact with the master template;

Figure 1'0 is .a plan View of the template fellower arm and follow-er mechanism;

Figure 11 is a front view lof Figur-e 10;

Figure 1:2 is an end elevation of 'Figure '11 looking in the direction of the arrow'shown in connection with Figure l1;

Figure 13 is a detail View Aof the servo-control valve employed in Figures 10, 11 `and 12;

Figure 14 is a vertical cross sectional vie-w taken -on the line I4-I4 of Figure ll;

Figure 15 is Va vertical cross section taken on the line |5-I5 of Figure 11; v

Figure 16 is a-detailed view of an enlarged template and correspondingly reduced follower Wheel; l

Figure 17 is a side view of a grinding head;

Figure 18 is a plan view -of-'the structure shown in Figure 17; f 1

Figure 19 is a detailed View of a grindingwheel and its dressing or truing device taken on the une lss-I9 of Figure 18; f

Figure 20 is a perspective view of the portion of the grinding head shown-in Figures 17 `and 18';

Figure 21 is a side View of Aa commutator control boX; l

Figure 22 is a cross section taken on theline 22-22 of Figure 21; K

Figure 23 is a diagrammatic view of a cycle timing hook-up 'for automatically starting and stopping the synchromotors shown by Figures 10, 11, 12, 17 and 18, which, inturn, operate :feed screws etc.

Figure 24is a wiring diagram'.y (Two sheets-.- Figures 24a and 24h).

The embodiment of the invention `asshown herein comprises the support Aor base indicated generally Vby the numeral l0 'substantially' in crucifix form and comprising the projecting arms |08, 1Gb, les and Mld. of the base or frame 'is the master turntable I2 Above the central portion.

mounted on a rotatable shaft l as best seen in Figure 6, and which is mounted in and extends through a slide indicated generally by the numeral I6, slidable in a vertical plane on a slideway I8 attached to vvertical support member it rising from, and attached to, the central portion of the base member I0.

Disposed above each of the four branches of the support members Ia, Illb, lc and Id respectively are a number of turntables 2Q. Since all of the turntables of all of the support branches are similarly mounted a description of the mounting and actuating means for one will suffice for all. As will best be seen by reference to Figure 4 each turntable 2i! is mounted upon a rotatable shaft 22, rotated as will be described to impart rotative movement to the turntable, and the rotatable table and its shaft 22 are mounted in a vertical slide member indicated generally by the numeral 24 which is slideable vertically on the slideways 26 comprised by support means 28 projecting upwardly from, and attached to, the base portion ila.

Rotational movement is imparted to the shaft I4 of the master turntable I2 by the worm wheel 30 fixed on shaft I4 and driven by worm 32 which is mounted on the shaft 3i! (Figures 6 and 7) and which is rotated by means of synchromotor 36.

Shaft I4 'is mounted in upper and lower bearings 38 and 40 comprising part of the slide I5, and movement of the whole slide assembly in a vertical plane is transmitted through an internally threaded nut 42 which travels on the :threaded shaft M mounted for rotation between the brackets 46 and 43 projecting laterally from the upwardly extending portion of vertical support member I9. Rotary motion is imparted to shaft M through the bevel gear 53 thereon which meshes with bevel gear 52 on shaft 5d of syncloro-motor 56.

Supported adjacent the lower end of shaft I@ is a cycle timing switch (commutator assembly) indicated generally by the numeral 58 which is driven by the rotation of shaft I through sprocket 69, chain 62 and sprocket Gil on cycle timing switch shaft S5.

The slides 24 on which the Work piece turntables 2D are supported are each actuated for movement in a vertical plane by a pair of internally threaded nuts 5S, each of which travels on the threaded shaft 68 which is mounted for rotation in the bracket 'I0 projecting from the support means 28. On shaft 65 is the bevel gear 'I2 which is driven from bevel gear M on shaft '|55 rotated by synchro-motor 18.

Rotatable shaft 22 for each turntable 2! has on its lower end the worm wheel Sii which is rotated by worm B2 mounted on shaft Sli which is driven by synchro-'noter B.

VMounted on the turntable 2t as by screws 8B is the work receiving holder 95 in which a work piece 92, such for example as is indicated in Figure d, is inserted 'and held while being ground down to size as will be described. As shown herein the work piece 92 is an air foil or bladewhich may be grooved at its lower end to engage corresponding grooves in the work receiving member 90 into which it may be inserted edgewise. As shown herein means are provided for contacting the upper end of the air foil or blade and lto hold it upon its work piece and prevent lateral vdisplacement while it is being it is being ground said means comprising a bracket Sli projecting upwardly from the slide 2d and havff and attaches to, base member I9.

ing at its upper end a slideway 25 in which a slide 98 is -adjustably positioned as by means of thumb screw |00.

Surrounding the turntable is a receptable or receiving pan |02 for a cooling liquid which may be supplied .to each grinding wheel through a nozzle IM of conduit |06 which is attached to a manifold lill thro-ugh which cooling liquid is pumped from sump |98 by means of pump ll, and returned from receptacle H32 to said sump |98 through conduit i2.

Upon the master turntable I2 a master template |I4 is pro-vided comprising an upper portion III!a the contour of which is to be reproduced in the work pieces 92, and a lower portion I Mb having a laterally projecting nange IMC secured to the turntable as for example by means of bolts IIB. Template is a facsimile of the desired product but is preferably proportionately larger. As shown in Figure 16 the dotted line ||5 indicates a template proportionally greater than the work piece 92, being contacted by a fol-k lower wheel IIl proportionally greater than the grinding wheel |56. However, in order to facilitate travel of the follower wheel around the ten plate and particularly its sharp bends or edges, and to provide additional rigidity for the ten plate, the template is built up by material added uniformly around its periphery tothe increased size indicated by the numeral I ll and the radius of the follower wheel is similarly decreased as indicated by the numeral I Ila.

Mounted above the base member IQ yare a number of pantognaphY arms indicated generally as H8, equal in number to the number of banks of work piece turntables, which is illustrated herein are four in number. Each pantograph arm has its inner end follower means adapted to follow the contour of "the master template and adjustable toward or away from the master template as is described below. VEach pantograph arm comprises the portion |20 pivoted intermediate its ends on the stud |22 projecting upwardly from column |24 which in turn rises from, Pivotally mountedV to the outer end of arm portion ISSa by the yoke |26 and pin |23, is the connecting arm |32v which may be automatically lengthened as will now be described. The outer end of arm |36 is pivctally connected by yoke |33 and pin II, to the connecting link |34. Rotation of the pantograph arm causes reciprocation of link |34, and actuated by movement of link |34 are the bell crank members |3S equalin number to the work piece turntables 2t, each having a bifurcated end |362L pivotally engaged engaged by said yoke |33 and pin ISI and being pivoted intermediate its ends on -a stud 38 projecting upwardly from column |20 which eX- l tends upwardly from the support means 28 (Figure 4). Each link |34 is p-ivotally connected at its inner end to the piston rod |35 extending from za piston member |37 contained in an air cylinder |39 which is .pivotally attached at its inner end by pivot IM tothe bracket |43 rising from support means 28 on base support member Ie. Cylinder |39 is connected to a source of compressed air to keep the follower in contact with the master template.

It may be noted that the distance from the pivot |38 of a bell crank arm 36 to the center of the shaft |44 supporting a grinding wheel Hifi is in the same ratio to the length of the pantograph arm portion between its pivot |22 and the pivot 252 of the follower wheel mechanism as the ratio .of the blade being ground to the master template. And the distance from follower arm pivot |22 to pivot `pin |28 is equal to the distance between pivot |38 of. the bell crank |36 and the pivotv pin 43|. The pantograph portion |22-252 is parallel to the vgrinding Wheel arm portion ISB-|44, :and similarly-portion l22-l'2'8- of the pantograjph arm is equal in length and .parallel to the grinding 4wheel arm portion i38|3|- Mounted at the -outer end of :each bell .cr-ank y|36 yis a hollow bushing |42 (Figures lll-.20) through lwhich extends a shaft |44, .on which ya grinding wheel |46 is mounted, shaft .|44 being driven from motor |48 through pulley |50 mounted on motor fshaft |52, belt i545, and pulley |55 ,mountedon the rear end of grinding wheel shaft |44.

Integral with .each bell crank |36 and positioned 'along one edge thereof (see Figure L8) is a slideway |60 on which is vmounted the slide |62 4which at one end supports the dressing tool |64 as will be described, `and which adjacent its other :endvis provided with -a bore |66 vinrwhich is positioned an `internally threaded `bushing :|69 into 'which extends the externally threaded motor shaft extension coupled to the shaft |12 of a synchro-.motor |14 by the-coupling :|16 (see Figure 24h, Section D). It will be understood that as shaft |10 is rotated slide |62will be moved to carry the ...dressing tool :|64 toward or away from the grinding wheel |46. A Vernier' scale |18 may be vprovided valong the slideway |6.0,'as .shown -in Figure 1-8, to indicate the loss in diameter of lthe grinding wheel .due to wear and honing, and for initially adjusting slide |62 (Figure 18) in relation to slide 260 (Figure ll). VThe dressing tool l|64 is rotatably mounted relative to slide |62, being fixed at the outerend of eccentric arm |80 which at one end is angularly formed and at its other end compri-ses a stud or pin vlill which is vrotatably received in bushing '|82 and which has secured at its router end the hub |84 of arm |86 which in turn is connected to the piston shaft |89 of cylinder |90. valve |9|a (or |9|b, |010, -or 10|?, Figure 24, Section C) is ,introduced into cylinder |90, armv |80 ls reciprocated as will be described, Ain an arcuate path causing the dressing tool to 'travel across the face of the grinding wheel -to Tdress it.

The connecting arm portion |30 of each pantograph arm (see Figure 8) com-prises three por 1 tions, namely, the tubular portion |96, the tubular portion |98, and the intermediate member 200 comprising the shoulder 202 from which the solid plug 204 extends in one direction into, and is force tted in, member |96, and from which the shank portion 206 extends .in the opposite direction through'the portion |96, said portion |96 having a recess 2.08 surroundingthe outer end of said shank. Within said recess is a colla-1: 2|0 having a portion of reduced diameter ,2:12 projecting outwardly from `the flange portion 2 hl, and surrounding said reduced portion, between the ange 2|-4 .and the inner end of said recess, isa coil spring 2|6. Saidv collar togetherfw-ith leather packing 2|8 and expanding washer 220 aresecured around the inner end of .said shank 206 by the nut 222. Spring 2|6 ten-ds'to urge the member 206 inwardly to bring the shoulder 202 ofmernber 200 against the forward end of member |96 thus leavingr any-lair chamber `22!` within portion |96. Communicating with chamber 223 within member |96, behind the assembly of said collar, packing Vand. w-asher, is a por-t 224 When air, by the operation Aof solenoid theouter yend ofwhichfis threaded for coupling' with .a .conduit 2-2|i1eading` to a source of air through manifo1d221andthe-:solenoid air valve indicated generally by the numeral 22B. As air is supplied .intothe chamber 223 the. said inter-` mediate portion |98 comprising, the shoulder 2.00, the plug 204 andthe shank- 206, will -move to the right as viewedinFigure 8, thus causing separation of member |98 from; member |96 and thereby lengthening.tina-arm against the force of spring 2| 6. -When air is exhausted from chamber 223 through .conduit A 2264 operation of valve member 22.8 the -forceof spring :2|6 :will serve to return lintermediate member 20.0 toits initial position carryingfwith itsaid portion |98 as desired through valvemeans 228 and Vthecontrol means shown in Figure 3;:(see-a-lso `.Figure 24e) and which-isdescribed'below.

In Figure 10 there isshownoneembodiment of follower meansadapted-to follow the contour of vthe master template -,|.-|'4. v'Ilhesaid follower means is vmounted on .the inside end of pantograph arm'4 |20. Saidipantographarm terminates at its innerend in aahub 250 in which is rotatably received the pivot stud- 252 formed` integrally with, .and projecting.; at right angles to, the slideway z254 which includes the vertical .arm 256 on which .synchro-'motor` 258 is supported. Mounted in the slideway254 is the slide member 260 and projecting from the front of said slide are .the 4opposed .ears 262 betweenr which the follower wheel264 is mounted as by means 'of the axial pin 266.' Radius .R (Figure 4,11) must always be in accurate .ratio to .corresponding radius of grinding `wheels |46; andradius ,r of follower wheel 2:54 .isin accuratelratio to `radius on periphery .of-grinding wheels |46 .(Figure 19). -The inner `endv of .slide 260 is provided-with v a bore 2.68 in whichis. positioned the .internally j shaft 218 of synchro-motor 25B. .'.rWhen synchromotor- 258 is actuated's'lide 260.is.moved to carry the vfollower wheel264towardor away from template |Y|4 .depending .upon the direction of rotation ofv synchro'fmotor 258-. Onslide 260 a Y Vernier scalev 21.3islgprovided to indicate the extent of movement of slide .260 in .the slideway 254.

Mounted for rotation on slide 260 is a slideway 280 .having the downwardly projecting pivot stud 282 which is received within bearings provided within slide 260. f l

Mounted on slideway200 is the slide mem-ber 284 which at its outer end `has the pair of vbearings 286 and .288 respectively disposed at right angles to the `sli-de 2.84 .and supporting pivot. pins 290 and 29.2 on the lower .extremitiesoff which are mounted the follower wheels 294 and 296, which, as shown, are somewhat smallerin diameter than the follower'wheelj 6.4- andfare aligned with the follower wheel^264,('see1ligure 15). Y

aeoaoes fixed to the arm 3,00`rising vertically from slideway 280. Said spring 299 thus tends to urge slide 284 to `constantly maintain wheels 294 and 296 incontact with the master 'template I I4for the purpose of maintaining the centerline of slide 260'accurately perpendicular to a line that is tangent to the surface of template |I4 upon which follower roller Y2l4'berfirs. Y

VWhen slideway 280 becomes angularlyrelated to the slide 260 (due for example to asharp bend in the prole of the template) the angular posi-v tion of said slidewayis'instantly corrected by a servo-hydraulic actuating cylinder 303 pivotally mounted on a stud 30| projecting from bracket extension 302 of arm |20, (Figures l and 12) controlled by a serVo-controlyalve 304 (Figure 13) which is of wellknown kind and which is actuated as follows; projecting rearwardlyrfrom slideway 280 is the arm 306=which is in contact at all times with the end of actuatingpin 300 which extends through-endend of the kservo-` Valve 304 and is urged 'outwardly by the spring member 3|0. Within servo-valve `304-and connected to pin 308 is Va'piston v3| 2 having the radial flanges 3 |4 and 3|6 wh'ich'divide the valve member into three chambers. Fluid is supplied to and from Valve 304 from pump 3|8, actuated by'motor 3|9, through conduits y32|) and 322 the latter of which comprises branches A322e andV 3221*, eand from valve 304 to one side lorthe other of piston 305 within cylinder 303throughconduit 301' or 359 depending upon the position of pistonl3|2 in valve 304. When the angularvposition of' slideway 280 is such that'its center line is alignedwitli` the center line of slide 260 piston 3 I2 within valve 304 remains in a "neutraP position, andthere is no AVmovement of piston 3L5V in cylinder 303. However, when this alignment is disturbed it is restored as follows: the change in pressure on pin 308 exerted through arm 305 causes a, change in the position of piston SI2/within valve '304- ,thereby causing acorresponding change in the position .of piston3`05 in cylinder30g3; Vthereby actuating piston rod 324, the outer end of. which is connected to stud 326 projecting from slideway-254, and thus 4swinging said slideway on its pivot stud 252 vuntil thecenter line 'of slideway 254 is aligned with the center line of slide 284.

Thus by actuationfof;synchro-motor3253y the follower slide 260 andffolloweriwh'eel '264v may beV moved toward'or away from templatejI I4v and thus maintain the, length of radiusfltVY (see Figure ll) in accurateratioj to corresponding radius of grinding wheelsvllflland bya'ction'of motor Y3I9 hydraulic cylinderf3v03 maybe actus-1 ated to restore alignment-between slidfewayV 2541 and slide 284 andY thusmaintain eente'rlinef'ofV slide 230 accurately perpendicular to a liney thatv is tangent to the surface of template ,I i4 upon which follower roller 264 bears.V f Y The cycle timing switch 58 referred' to above comprises shaft 240 which has mounted thereon the three commutator disks 2402, 240i), and 240.

(Figure 21). Y v Y Shaft 240 is driven from shaft S (which is driven from shaft I4 as described above). Shaft 35 has on its other end a gear 24| which through its intermediate gear` 243 actuates gear 245 on shaft 240. The upper Vcommutator disk 240a has thereon' a Contact segment 24'|,(fsee Figure 24e,`

Section C), whichas the shaft240 revolves ienee the diagram is divided into sections'A, Bp

s, connected to lead 4|I, and a contact ring 25|' which is in continuous contact with brush .253 which is connected to lead 4|2a. Similarly commutator disk 240b has thereon the contact segment 255 which is contacted periodically by brush 25'! which is connected to the lead 4|0, and a contact ring 263 which is in continuous contact with brush 265 which is connected to lead 4|3. Similarly commutator disk 240c has thereon-the contact segment 267 which as shaft 240 revolves makes contact periodically with brush 259 which is connectedv to the lead 4|5, and Contact ring 215 which is in continuous contact with'b'rushZTl which is connected to lead 4|2b. The function of the cycle timing switch is described further in Yconnection with the wiring diagram, Figure 24, and Figures 2, 3 and 23, respectively. Y Y

As shown in Figure 2 a/source of compressed air-'229 is connected through reducing valve 23| and solenoid air Valve IB!a (see Figure-24a) to the manifold 235, and through branch conduits'y 23'! to the cylinders |90, which, asV shown in Figure 20, are connected tothe vdresser too-l arms |36 of one bank or series for rotatingY the dressing tools |64 carriedV by saidarms respectively, and` causing them thereby toy eect the dressing operation. The solenoid air valve liila'iscontrolled by relay 4|8 (see'ligure 24a) "which is connected with the commutator ring 242C by leads @I5 and 4|2b from transformer V4&8.

As shown in Figure 3a Vsource of compressed air 230 is connected through conduit 232 andreducing valve 234 and solenoid air valve "228 and conduit 232EL vto the manifold' 252i, and through branch conduits 226 to the air chambers 223in connecting arm |30 attached: tothe pantograph arms |20. As shown in Figure'ZiSection C, solenoid valve 228 is energized throughY magnetic contacter SI5 which is controlled lby relay coil 4I4, relay 4|4 being connected' rorn'lead 4|@ through relay coil 4|4,through leadV 4| I to commutator disk 24084 on shaft 240 of cyclev timing switch 53 and through lead `fl|2ab toline M2, kMil and 4|2 beingv opposite ends of the secondary of transformer 408. Y

Figure 23 shows'the commutator disk 240b be'- tween leads 4H) yand 4|3 and energized from transformer 438, and connected through contactor unit 428 with vthe induction motor `4138, Variable speed unit 440, and synchro generators 442, 2422, 442c and 4421i.' See Figure 24a, section C and-'Figure 24h, sectionfD.

Wiringdiagram Y Y' Y"Figures 24a and 241 Ytaken togetherl show a wiring diagram for my machine. For conven- C, D, E, and F, deiined by dotted lines' and 'indicating parts of the diagram'which relates respectively to: A;V rotation of. turntables; B,-'o per ation of vertical feed screws; V@sequence control of grinding wheel retraction andv dressing opere ofl follower slide; E, rotation of 'grinding wheel power source.

motors; and F, rotation of motorv on Nservo fluid supply pumpand motorsrdriving coolant pumps.

Incoming lines 330,332 and 33,4 supply the machine with electrical energy from asuitable These lines'are connected'to line side of device SSW, which gis a fused safety switch. The bottom or load, side of this device has leads 338, 340 and342rconnected to it. These Vleads are the supply'leadsf for all Sec- 9 tions shown by the wiring diagram, and bear these numbersthroughout the wiring diagram;

Section. A

In Section 'A, leadsA 33.8, 34:6.and 34,2- connect to studs on linel side. ofr S-pole magnetic contactor 344. When start button 3146:.is depressed it completes the circuit supplying the coil TT which operates the said contacter.` The three contacts marked. 348 .then close, to supply:l current through leads 35.0, 3.512 and 35,4 to. the induction motor 35.6, which drives the variable speed unit 358, which in turn actuates and controls the roltor of synchro generator 368, which translates mechanical power to electrical. energy which is transmitted through leads 362', 36.4' and 366 to synchro motor 36 which rotates the master turntable l2, and to synchro motors 86e, 86., 86 and `86d which rotate the four series or banks of work piece. turntables 28, shown'. in the embodiment of the invention describedl herein. At the same time, the auxiliary contact marked 361 closes to complete the holding circuitfor coil TT,

The` normally-closed contacts 368 are thermally-operated contacts. adjacent to heater ele.- ments 368 in the; leads going out to the motor 356 and remain closed unless an. overload or fault occurs to cause the motor to draw an excessive amount of current. Should this occur, these 'contacts would open and interrupt the circuit. to the coil, causing the magnetic contacter 344 to drop open and remove power to the faulty equipment. Similar thermally-operated. contacts are shown elsewhere in the circuit without separate reference since ltheir function will be obvious.

Lines 338 and 348 also go to primary side of transformer 316. The secondary side. of. trans.- former 318 supplies the fields. on synchro gen.- erator 368 and turntable synchro. motors 36,. and 86a, 86h, 86c and 86d, through leads' 312 and 314.

Section B Leads 338, 348 andl 342'. also supply power to studs on magnetic reversing contactor 316. When up button 318 is depressed, the FU, or up feed, coil circuit is completed and. three main contacts 388 close to supply current from lines 338, 340 and 342 to lines 382', `384 and 386. respectively to rotate induction. motor 388, which,

through variable speed drive 398 actuates the rotor of synchrov generator 392to cause synchro motor 56, which operates the vertical feed screw 44 of the master turntable l2, and synchro mo.- tors 18a, 18h, 18.c and 18d, 'which operate the ver! tical feed screws 68 of the vwork piece turntables 20, to rotate in up direction. The auxiliary contact 394 on FUI is also closed to complete the holding circuit for FU. coil; maintaining contacts 388 as long asr up limit switch 395 is closed. When upper limit of vertical travel is reached the upv limitA switch is operated. This opens normally closed up limit switch contact 395 to drop out the FU"".contactor which stops vertical feed up Thisv also closes normally open up limit switch contact 395'f1'to complete, the FD, or down feed, coil. circuit, if the ARS (automatic reversing switch) -is closed; other lwise, the said vertical feed screw motors will re..- lmain at rest at. the end .of travel in "up direction. If ARS is closed FD coil picks -up to close the three main FD contacts 480, and this Vreverses the rotation of motor r3.88 .driving the synchro generator .392' by supplying current lfrom 3.38 to 386, 340 to .384, and 342 1:0382. The said vertical' feed screws lthen operate lin down di.-

lrection. until. the. down limiter?` travel is reachedwhen down limit switch 4365 is;. opened and 405e, normally: open, limit switch ,.closcs, and the,

direction of travel is again. reversed.

The operation when down push button 4 02 is first depressed, or. when stop push button.v 484 is` depressed, will be understood. from the.

above description and Figure 2d, and' need not; be described in detail.

Lines 338 and 348 also go to the primary side of. transformer 406,. the Seeondary side of. .which supplies the flelee` onernehro generator 392.. end Synchro motore 56. env'lt. 13px' 'lai' ma: 7134 through leerde-401 %1.e.`4091 section '-off From mansion-ner 40.8. .Seoondery Gomes the. control power leads 4|.8and 4t2 between Which ere ooneeoted the. oommute'or disks 240% 24F and 24.8.0 of cycle timing. lswitch 58rv (see Figure 21.).A and the solenoid volte 228 .which suelolie eir'to the portions ltoof the oeotoerepli orme fier lengthening them and they solenoid valves lille, iSIb, ISIc and lilld (see also Figure 3), operating the four series of dressing tools associated respectively with the grinding wheels |46Y of the four series of grinding wheels. ,for the Work nieoes on the fourseres or banks-oi turntables It Coil. M4, which is a pilot relay on retraction arvalye 228, is energized. whenever both contact seg: ments 241 and 25! on oommutetor disk Zine/ere under their brushes.- Whenever the Girelli@ through this loeil' is o l'oeedoit closes. eonteot 416 thus causing the portion |38' of the. pantographl shownl in Figure 8- to loe lengthenedto free the grinding wheels @-462 from the work pes'pre: liminary tothe wheel dressing operation,

Coil 4I8.wh-i oh ,is the pilot reler on. the .dresser mechanism solenoid valves lgle, |811?, [819' and 'Slt ie energized Whenever beto oommotetor segments on commutator disk 24109 of. cycle tim: ing Switch 58 are under their brushes.v Whenever the circuit through. coil. 4.18. is closed it closes the contacts 420, 42-f, 424' Wnd 426119 energize the Asaid solenoid Valves lIfile,119.,.1?, i912c and |315?.

Gommutator disk .2.4b'oompletee the eirellit to thel magnetic contacter unit 4'28.119WI1 3699.109 ((DY.

Section D Commutator disk 241)b completes` the circuit to the .coil f-FN of contacter u-nit 428 to close the contacts 43-wherrboth contact segments of commutater disk 2401* are under their brushes. When closed. contacts 430' supply current from main supply lines 338, 348. and 342 to lines 432., 434 and 436 which .supply current to induction motor 438- Which serves through the variable speed drive unit 448 to actuate synchro generators 442e, 4`42b, 442-2 and 442d which in turn aci utate follower Wheel feed screw motors 258e, 25810, 256c and 2588-; and synchro. motors 114 (twenty: four as shown in Figure. 24.-siX foreach. bank offdressi-ng tools |64) for .operating thev `dressing tool feed screws'. |10 (Figure 18).

rLines .434 and 436 .also supply current; to .the brake release solenoid .coil 444' on the shaft .(,varie able speed' drive shaft) of.' induction Ymotor A38'.

Between icommuta'toradisk 24.81 .o f .Section "fCf and the'contactor 4.28' .of .Section Df a manual switch-.446 is connected and by yoperation .of itsA three push buttons, ,4.48 for vvnormal feed, 4556301'. reverse, and .4.52 4for stop,lgm anual con.- .trol may besubstituted for .and given precedence over the commutator sequence. .control described above. Forreverseoperation'push 'button 45,0 is

manually closed causing coil FR to close the Section E When energizing the grinding wheel motors 148 (equal in number to the number of grinding wheels) current is supplied from the main supply lines to a magnetic 'contactor unit 410. Coil GD is energized by depressing start push button 472 which causes the contacts 414 to close and thereby supply current from main supply line 338 to lead 4.16; from main supply line 340 to lead 418; and from main supply line 342 to lead 480, thereby supplying current to the grinding wheel motors 148. The circuit through coil GD remains energized until stop push button 402 is depressed.

Section The motor 319 vwhich operates pump 318 supplying uid to servo-Valves 304 (see Figures 11, 12 and 13) is started by closing manual circuit breaker 490 from main supply lines 340 and 342 to motor leads 492 and 494. Pump 318 is shown (Figure 13) provided with manifolds 311ia to reduce the number of pumping units required.

y The coolant pump motors 496e, 496b, 496c and 441id (Figure 4) are started by closing fused safety switch 498 which supplies power from line 340 to lead 500 and from line 338 to lead 502 which supplies power to fourindividual circuit breakers 504, 506, 508 and 510, one for each pump, circuit breaker 504 being connected to motor 496a by leads 512, 514, circuit breaker 505 being connected to motor 491ib by leads 516, 518, circuit breaker 503 being connected to motor 496c by leads 529, 522, and circuit breaker 510 being connected to motor 4913d by leads 524, 526. These circuit breakers are normally closed and open onlyon overload, or, are opened manually if it is desired to shutoff the coolant on one or more bank of grinders.

The operation of my machine is as follows;

after the master template and work pieces (shown herein as blades) are attached to their respective turntables, and the dressing tool slide 162 of Figure 18 and the main slide 269 of the Vfollower wheel mechanism of Figure 11 are initially set to their proper relative positions, and the servo fluid supply pump motor 319 (Figure 1S) has been started by the operator closing circuit breaker 490 (Figure 24h, Section F) and compressed air has been admitted to air cylinders 139 (see Figure 1), the operator starts the grinding head motors (see Figure 17) by depressing grinding wheel motors start button 412, and starts coolant pump motors 496e, 496i), 496c and 496d (see Figure 4) by closing switch 498 (Figure 24h, Section F). The operator next starts rotation of the turntables 12 and 2l)` (supporting the master template and blades respectively) by depressing the turntables start button 346. lThis causes operation of a motor 356 which rotates synchro generator 360 through variable speed drive unit 358, and the synchro generator 360.causes synchronous rotation of the synchro motors, 36 and 864,861), 86c and 86d that rotate the various turntables (see Figure 1). The oper- Vator then depresses push button 318 .or 402 for up or down movement of the vvertical slides'that' support the turntables 12 and 20 of the masterl template and the work pieces respectively. This causes operation of a motor 388 which rotates a synchro generator 392 through a variable speed drive unit 399 and the synchro generator causes synchronous'rotation of synchro motors 56 and "15a, isb, 'i90 and 18d that rotate the feed screws 44an'd 69 that loperate the vertical feedof the master and work piece turntables. The 'direction of the vertical feed is selected by the' operator, by pushing the up feed button 318 or theV down feed button 402 and such direction lselection depends uponwhether the bladesare to be ground from the tips, toward the Shanks," or vice versa. Assuming that, for the'rst grinding operation, the direction of feed is from the blade tips toward the blade Shanks, .then for theV second operation the direction vof feed would be reversed andv would be from the blade Shanks toward the blade tips, and .the direction of feedlwould be reversed for each succeeding'grinding operation. Suitably positioned limit `switches395 and 405 (see Figures 6, 7 and 24), automatically stop, or,

' stop and reverse, the direction of rotation of motori 388 which in turn'reverse's direction of rotation of synchro Agenerator 392 and. causes reverse rotation of the synchro motors 56 and i821, '1611,180 and 78d.. f The operation of the grinding wheel dressing mechanism is controlled automatically by the commutator disk 240c of cycle timing switch 58 (see Figure 6, and Figures 21 and. 22) the shaft of which is rotated at the desired speed from the vertical shaft 14 of the master template turntable. The desired number of revolutions of the cycle timing switch means in relation to the revolutions of the master template turntable, in'actual practice, will have to be determined by experiment and will depend upon how often the grinding wheels will require dressing in relation to a revolution of the blade being ground. The desired revolutions of the cycle timing switch in relation to the master template turntable are readily obtainable by varying the ratio of the sprocket wheelsv 60 and 64 that drive the cycle timing switch (Figure r6), and/or by varying the ratio of the gears 241, 243 and 245 shown by Figures 21 and 22. The automaticoperation of the grinding wheel dressing mechanism is described below. The entire operation should Ybe performed as rapidly as practicable, so as to minimize the period of time thatV grinding wheels are out of contact with blades being ground.

YWhen contact segment 24'1`of the upper commutator disk 241)a makes contact with its brush 249,'airris automatically 'admitted to the air chambers 223 in the pant'ograph arm portions (Figure 8), thus causing this arm portion to klengthen and thereby swing the grinding wheels 146 clear of the work being ground. The contact segment 24'1 of this commutator disk is suiciently long to prolong this step-until the two subsequent steps in the wheeldressing operation are completed. Y

The contact segment 255 of the mddlecommutator disk 2413.b then' rotates intocontact with its brush 251.V This vcauses 'motor '438, driving through a variable speed unit 440, to rotate the four synchro generators 4422, 442D, 442c and 4424; and each generator, in turn 'causes synchronous rotationrof synchro-motors11`14 irotating feed screwsl 175 that: move theVV slides162 supporting grinding wheel I: dressers Vtoward the grinding wheels 146l to be' dressed (seeFigures l8'a`nd'23) accepte and of synchro motors' 258e, 2585, 258c and 258@y which operate feed screws 272 to move the main slide 266 of the follower wheel mechanism (Figure 1I) away from the master template H4 an amount proportionate to the wear of the grinding wheels. (Assuming that the ratio between the master template and the blade being' ground is :1, the relative movement of the two aforementioned slides will also be 10 f1.)

Immediately after' the preceding operation is' completed, the Contact 'segment 261 of the lower commutato'r disk 240e makes' contact with its brush 269 which energizes solenoid-operated air valves lilla, mlb, I Qi'i and Igld, and thereby causes air to' beadrnittedto th air cylinders ist shown by Figures 2 and 17, thereby causing the wheel dressers |64 to dress the grinding wheels |46. Whenthe contact segment 261 of the commutator disk 240C revolves Past its brush 269 the solenoid-operated air' valves lele, leib', lillc and leid, are dee-energized and automatically allow the air to exhaust from the air cylinders i90, permitting the wheel dressers 'to return to their norrnal positions, as shown by Figure 17,

whenv the alcove operation is completed, the Contact segment 241 of the upper commutator diskl 241ia revolves past its brush 24s, and the solenoid-operated valve 22's involved Ais de-energiaed and allows the' air to exhaust from the air chambers 223 in portions 130 of the pantograph arl'ns (Figure 8v), and said arms return (shorten) to norrnal length, permitting the grinding wheels to again ineke contact with the work being ground, and the cycle of operation is repeated automatically as long aS master template turntable shafty I4 Continues to rotate.

After the vprocessed work pieces are reinoved from turntables' 2i), new worl' pieces to be groliil'dlhay be attached to Said turntable, and il they are diiferent in shape or siae from the ones previously processed a new inast'er template H4 will he substituted on inasterr turntable l2. Another grinding operation may then be initiated and performed as described above.

'It will thus te seen that there has been provided this' invention a I'ne'thod and apparatus in which the various objects hereinabove set forth together with inany thoroughly practical advantages are successfully'achieved. M variouspossible embodiments might 5e iliade of the' niechanicalfeaturs of the above invention and as the art herein described might be varied in various parts, all without departing from the scope oi the invention, it is to b e understood that accompanying drawings is to be interpreted as illustrative and not in a liiniting sense. v The invention described herein iiiay be manufactored and used by or for the Government of the United States of America for governmental purposes 'without the 'payment of any royalties thereon or therefor.

What l claiin ist y y 1. Aniacliinevtool for simultaneously grinding several identical work pieces comprising a base having an enlarged central portion and an elongated arm projecting therefrom, a master template, supporting means for' said master template mounted upon the enlarged central portion of said case, a plurality `of supporting means for work pieces to be ground mounted atv spaced intervals yalong said relongated arm, grinding wheels equal in number to said work piece supporting means'v movably 'mounted upon said elongated ann and positionedadiacent to the 'respective 'work piece supporting ineaiis, a follower inovaloiy mounted' upon the central por'tlonof said base adjacentjto said master template and arranged to travel over' its surfacarneans'mcluding a con` necting'arm `interconnec'ti'ng said follower and said Agrinding wheels for movement in unison toward or away from said template and said work piece supporting means' respectively, means for driving said grinding wheels, and means fornioving the' respective supporting means for said template and said 'work pieces in synchronism relatively to said follower and saidl grinding wheels respectively, both hor'lioiftally' and vertically.

.apparatus as claimed inclaini l, including. means y operablev` at predetermined intervals for simultaneously moving all of said grinding wheels out of engagement withtheir respective work pieces and into 'a retracted position for a short tilne interval, truing .devies individual to each grinding Vwheel including support means for said truing devici'eisindividually', each said support means being movable relative tothe grinding' wheel with which it is associated and including means for swinging said tiuhg device in' an arcuate path, and control 'Inealls for moving Said support means' to bring said truing devices into Contact with the respective grinding wheels while they are' in their retracted position and to swing said truingdevices in an arcuate path around the periphery of the respective'grinding wheels.

3. apparatusv 'as' claimed in'claizn 2, wherein each grinding wheel is mounted on a corresponding supp-ort arin, andgin addition, each support means comprises aslide to which each truin'g device is attached, said slides being mounted on the respective support arms, feed screws individual to said'slide's, said'feed screws also being mounted on the respective support farms,l and means for rotating said feed screws operative to advance and retract said slides. Y

4. Apparatus a's claimed in claim 2, wherein veach grinding wheel is mounted 0n a corresponding 'support arm, and in addition, each support means comprises a slide mounted on each said support arm, a melnb-er rotatably mounted in a bearing attached to ca ch said slide and larranged to support a tring'- device therein, feed screws individual to said slides also mounted on vthe respective supp-ort arms', means for rotating said feed screws operative to advance and retract said slides,- and separatey means operative to impart reciprocative arcuate 'motion to said rotatably mounted truing' device supporting members to cause the truing devices to swing in arcuate paths across the respective grinding wheels'.

5. The device as claimed in claim lv in which thefolloweris mounted on a Vslide` and there is provided'a slideway for the slide,V means for advail'cing and retracting said slide, and synchro- 'inotor means for actuating said advancing and Yreti'acting means individually,-

6. The vdevice as claimed in claim 5 comprising also an auxiliary slide 'mounted on the follower support slide and comprising at its outer end two arlnsrollers carried by said arms respectively and disposed so as -tocontact said template on opposite sides of said follower, said auiiiliary slide being pivoted around an axisextending at right angles to the follower support slide, and means urgingv saidv rollers into contact with said template.

7. .The'device as clan'iedn claini '5 comprising also 'an aui'iliaryA slide mounted Aon the' follower sunnort slide andy niprising "atjitsY outer-'end two arms, rollers'carried by saidarmsrespectivelypand disposed so as to contact said template ron, opposite sides of said follower, said auxiliary slide being pivoted around an axis extending at rightangles to the follower support siide, and spring means urging said rollers into contact with s aid template said follower support slide being pivotally mounted, a servo-hydraulic cylinder for rotatingrsaid main slide about its pivot-a servo-control valve for controlling said servo-hydraulic cylinder, and a lever projecting from said auxiliary slide and adapted when the center line` of the auxiliary slide is moved angularly with respect to the center line of said main slide to actuate said servo-control valve causing the servo-hydraulic cylinder to revolve said main slide and restore the main slide to a position in which its centerline is aligned with the'oenter lineof the auxiliary slide and is perpendicular td a line tangent to said template.

SJITlie device as claimed in claim comprising also' an' auxiliary slide mounted on the follower support slide and comprising at its outer end Vtwo arms',i.rollers carried by said arms respectively and disposed so as' to contact said template Von.. opposite sides of said follower, said auxiliary slide being pivoted around an axis extending at right angles-to the follower support slide, and spring means urging said rollers into contact/with said template said follower support slide being pivotallymounted, means for rotating'said main slide about its pivot, other means for controlling said main slide rotating means, and a` lever projecting from said auxiliary slide and adapted when the center line of the auxiliary slide is moved angularly with respect to the center lineof said main slide to actuate said means for controlling said main slide rotating means causing said main slide rotating means to revolve said main slide and restore the main slide to a position in which its center line isaligned with the center line of the auxiliary slide and is perpendicular to a line tangent to said template.

9. The apparatus as claimed in claim 1, including means'operable at predetermined intervals for simultaneously moving all Yof said grinding wheels out lof engagement with their respective work pieces and into a retracted position for a short time interval, truing devices located adjacent to each of said grinding wheels and movable while said grinding wheels are disposed in their retracted position to lbring the truingdevices into contact with the grinding wheels to dress them simultaneously, and means individual to each truing device operative at the desired time to move said truing devices toward or away from their respective grinding wheels.

10. The device as claimed in claim 1 in which the template and follower are uniformly larger thanrthe desired finished product and the grinding wheels respectively,Y and the movement of the template supports vertically is proportionately greater than-the: movement of the work supporting means respectively.

1 1; A devicefas claimed in claim 1 in which said connecting arm" interconnecting saidV follower and, said grinding wheels is variable in length, andn means are provided for varying the length of said'arm at timed intervals.

12. The apparatus'gasclaimed in claimY 1 in which the template is proportionatelygreater in size than the desired final product, and control means-is provided whereby the movements of said vtemplate 'in a horizontal and inra vertical plane a'rejpiroportionately;greater than the corresponding movements of the .work pieces respectively.

13. The deviceias claimed in claim 1 in which the said follower is adjustable in length, and means are provided for adjusting the length of said follower to maintain the eifective radius of swing of said follower in relation to the radii of said grinding wheels. Y vi 14. The device as claimed in claim l in which the said follower is adjustable in length, and means are provided for adjusting the length of said follower in proportion to changes of the radii of the grinding wheels.

l5. The device as claimed in claim 1 in which the length of said connecting arm may be modied, and means are provided for modifying its length at timed intervals.

16. The device as' claimed in claiml in which said connecting arm. comprises a telescopic portion, a iiuid chamber within said portion, a source of fluid connected to said chamber, and means for causing the admission or discharge of fluid from said chamber at predetermined intervals to modify the length of said connecting arm.

17. A machine toolfor simultaneously grinding several identical lwork pieces comprising a base having an enlarged central portion and a plurality of elongated arms projecting therefrom, a master template, supporting means for said master `template mounted upon the enlarged central portion of said base, a series of supporting means for work pieces to be ground mounted at spaced intervals along each said elongated arm, 'a series of grinding wheels equal in number to said work piece supporting means movably mounted upon each said elongated arm and positioned adjacent to the respective work piece supporting means, a plurality of followers equal in number to the number of said elongated arms movably mounted upon the central portion of said base in spaced positions adjacent to said master template and arranged to travel over its surface, means including a connecting arm interconnecting each said follower and one series of grinding wheels Yfor movement in unison toward or away from said template and said work piece supporting means respectively, means for driving said grinding wheels, and means for moving the respective supporting means for said template andV said work pieces in synchronism relatively to said follower and said grinding wheels respectively, both horizontally and vertically.

18.' A machine tool for simultaneously grinding vseveral Videntical work pieces comprising a master template, supporting means for said master template, a plurality of supporting means for work pieces to be ground, grinding wheels equal in number to said work piece supporting means and positioned adjacent to the respective supporting means, a follower located adjacent to said template and arranged to travel over the surface of said template, means including a connecting arm interconnecting said follower and said grinding wheels for movement in unison toward or away from said template and said work piece supporting means respectively, means for moving the respective supporting means for said template `and said work pieces in synchronism relatively to said follower and said grinding wheels respectivelm both horizontally and verticallymeans for driving said grinding wheels, a

wheelv dressing device mounted adjacent to each said'grinding wheel, and means operable at predetermined intervals for simultaneously moving all of said grinding wheels out of engagement with their respective work pieces and into engagement with their respective dressing devices to dress the surfaces of said grinding wheels.

19. The device as claimed in claim 18 in which each grinding wheel dressing device is mounted on a slide and there is provided a slideway for eachrslide, means for advancing and retracting each slide, and synchro-motor means for actuating said advancing and retracting means individually. v

20. A machine tool for simultaneously grinding several identical work pieces comprising a base, a master template, supporting means for said master template movably mounted upon said base, a plurality of supporting means for work to be ground also movably mounted upon said base, grinding wheels equal in number to said work piece supporting means mounted upon said base and positioned adjacent to the respective work piece supporting means, a follower mounted upon said base adjacent to said master template and arranged to travel over its surface, linkage means interconnecting said follower and said grinding wheels for movement in unison toward or away from said template and said work piece supporting means, means for driving said grinding wheels, means for moving the respective supporting means for said template and for the work pieces in synchronisrn relatively to said follower and said grinding wheels respectively, both horizontally and vertically, biasing means for maintaining said follower and said grinding wheels against said template and the work pieces carried by said work piece supporting means respectively during grinding operations, said biasing means including an air cylinder mounted upon said base and operatively connected to the linkage means interconnecting said follower and said grinding wheels, and means incorporated in said linkage means operative periodically to change the length of said linkage means to move said grinding wheels out of engagement with their respective work pieces without disengaging said follower from said template.

21. A machine tool for simultaneously grind-` ing several identical work pieces comprising a base having an enlarged central portion and an elongated arm projecting therefrom, a master template, rotatable supporting means for said Cil master template mounted upnthe enlarged central portion of said base, a plurality of other rotatable supporting means forwork pieces to be ground mounted at spaced intervals along said elongated arm, means for rotating said supporting means in synchronism, grinding wheels equal in number to said work piece supporting means pivotally mounted upon said elongated arm and positioned adjacent to the respective Work piece supporting means, a follower pivotally mounted upon the central portion of said base adjacent to said master template and arranged to travel over 'its surface, means interconnecting said follower and said grinding wheels for moving said follower and said grinding wheels respectively in unison toward or away from said template and work pieces on said work piece supporting means respectively, and means for raising and lowering said template supporting means and said work piece supporting means simultaneously and proportionately.

22. The device as claimed in claim 21 in which the said means interconnecting said follower and. said grinding wheels is extensible, means for exerting pressure lengthwise of said interconnecting means to extend it and thereby move the grinding wheels out of contact with said-work pieces without moving said follower from said template, and control means for exerting said pressure and relieving said pressure at predetermined intervals.

HOWARD H. MORRIS.

REFERENCS CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,363,238 Duchemin Dec. 28, 1920 1,840,231 Harrison et al. Jan. 5, 1932: 2,102,505 Berthiez Dec. 14, 1937 2,151,743 Chladek Mar. 28, y1939 2,445,971 Rosen July 27, 1948 2,506,264 Borrup ..-s May 2, 1950 FOREIGN PATENTS Number Country Date Great Britain July 15, 1941 

